Free browser-based PHP IDE
smashingapps.com
smashingapps.com
As awesome as this is, I can't imagine the target audience (people who do web programming) be willing to put their credentials for their own sites into another site. I know I don't even trust my credentials for my web server on my own local machine.
It's not that I'm putting sensitive information out there, it's just a strange kind of trust issue.
On the plus side, I can't imagine it being that hard to add syntax highlighting for additional languages.